I have three gauges in the radio slot but I soon removed the boost gauge as I couldn't take a peek at it fast enough. I have oil pressure, oil temp and engine temp in mine - all smiths so they look period. I put my boost gauge in one of the pods designed and moulded into the upper steering column cover.

That way I can keep an eye on it much much easier - it lines up with the original gauge in the dash which is hidden behind it - works a treat.